Purinergic signaling, a type of extracellular signaling mediated by purine nucleotides and nucleosides such as ATP and adenosine, involves the activation of purinergic receptors in the cell and/or in nearby cells, resulting in the regulation of cellular functions. Most cells have the ability to release nucleotides, which generally occurs via regulated exocytosis (see Praetorius, H. A.; Leipziger, J. (1 Mar. 2010) Ann Rev Physiology 72(1): 377-393). The released nucleotides can then be hydrolyzed extracellularly by a variety of cellular membrane-bound enzymes referred to as ectonucleotidases.
Ectonucleotides catalyze the conversion of ATP to adenosine, an endogenous modulator that impacts multiple systems, including the immune system, the cardiovascular system, the central nervous system, and the respiratory system. Adenosine also promotes fibrosis in a variety of tissues. In the first step of the production of adenosine, ectonucleoside triphosphate diphosphohydrolase 1 (ENTPD1), also known as CD39 (Cluster of Differentiation 39), hydrolyzes ATP to ADP, and then ADP to AMP. In the next step, AMP is converted to adenosine by 5′-nucleotidase, ecto (NT5E or 5NT), also known as CD73 (Cluster of Differentiation 73).
The enzymatic activities of CD39 and CD73 play strategic roles in calibrating the duration, magnitude, and chemical nature of purinergic signals delivered to various cells (e.g., immune cells). Alteration of these enzymatic activities can change the course or dictate the outcome of several pathophysiological events, including cancer, autoimmune diseases, infections, atherosclerosis, and ischemia-reperfusion injury, suggesting that these ecto-enzymes represent novel therapeutic targets for managing a variety of disorders.
CD73 inhibition with monoclonal antibodies, siRNA, or small molecules delays tumor growth and metastasis (Stagg, J. (2010) PNAS U.S.A. 107:1547-52). For example, anti-CD73 antibody therapy was shown to inhibit breast tumor growth and metastasis in animal models (Stagg, J. (26 Jan. 2010) PNAS U.S.A, 107(4):1547-52). In addition, the use of antibodies that specifically bind CD73 has been evaluated for the treatment of bleeding disorders (e.g., hemophilia) (U.S. Pat. No. 9,090,697). Recently, there have been several efforts to develop therapeutically useful CD73 small molecule inhibitors. For example, Bhattarai et al. ((2015) J Med Chem 58:6248-63) have studied derivatives and analogs of α,β-Methylene-ADP (AOPCP), one of the most metabolically stable, potent and selective CD73 inhibitors known, and purine CD73 derivatives have been reported in the patent literature (WO 2015/164573). However, the development of small molecules has been hampered due to, for example, less than ideal metabolic stability.
In view of the role played by CD73 in cancer, as well as a diverse array of other diseases, disorders and conditions, and the current lack of CD73 inhibitors available to medical practitioners, new CD73 inhibitors, and compositions and methods associated therewith, are needed.